I would get a second opinion from a Board Certified Foot and Ankle Orthopaedic surgeon before having the surgery. If he/she concurs with the DPM's surgical plan then you can feel confident in going forward. If there is a difference of opinion you may want to seek a third. I have heard of "older" people having had this surgery and doing well. I kinow there is at least one person who posts on here who is I believe in their late sixties.
I would also ask your surgeon how often he or she performs these surgeries, how often have they had patients your age undergo the surgery and what the outcomes were for them. I would ask if there are any particular concerns about rehabilitation because of your age. If you are in otherwise good physical health and are active without any other underlying medical conditions that would impede healing, I see no reason why your age would keep you from doing well with the surgery. The alternative isn't very appealing! If you are very active I don't imagine you would want to be hindered by braces, boots, or wheelchairs the rest of your life.
Best of luck to you. Let us know how things turn out.